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Editors' Choice

Marine hydrocarbon cycling revealed

Caroline Ash

Ocean-dwelling Synechococcus cyanobacteria can produce hydrocarbons

PHOTO: EYE OF SCIENCE/SCIENCE SOURCE

Up to 4 million tons of crude oil leak into the oceans every year as a result of human activities and natural seepage. But hydrocarbons and hydrocarbon-degrading bacteria abound even in waters minimally polluted by oil. Knowing that cyanobacteria have the capacity to produce long-chain alkanes and are abundant in surface waters, Lea-Smith et al. set out to determine whether these bacteria are a significant source of hydrocarbons. It turns out that together, the cyanobacteria Prochlorococcus and Synecoccus produce up to 700 million tons of hydrocarbons per year via their alkane biosynthetic pathways. These cyanobacteria may help to sustain hydrocarbon-degrading bacteria and thus unwittingly help to mitigate some fraction of anthropogenic pollution in the ocean.

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1507274112 (2015).

Immunogenetics

How heritable is autoimmunity?

Laura M. Zahn

For many complex diseases, a mix of a person's genes and their environment determines their susceptibility, with genetic influences often playing a greater role in children. Li et al. investigated how genes contribute to the development of autoimmune diseases such as type I diabetes and ulcerative colitis in children. By comparing 5000 pediatric autoimmune pediatric cases with over 36,000 healthy controls, the authors determined that genetics contributes substantially to susceptibility to autoimmune diseases. The highest heritability was observed for type 1 diabetes and juvenile idiopathic arthritis, whereas the environment played a greater role in susceptibility to lupus. Similar to autoimmunity in adults, heritability correlated highly with genetic variation in the major histocompatibility region.

Nat. Commun.6, 8442 (2015).

Biomineralization

The pathway to mother of pearl

Nicholas S. Wigginton

Abalone shells grow from amorphous calcium carbonate precursors

CREDIT: P.U.P.A. GILBERT

The material inside mollusk shells, nacre, is remarkably tough and also gives the shells their sheen. Nacre is a hybrid of aragonitic calcium carbonate and an organic matrix, but it's unclear how it starts growing. Using synchrotron-based microscopy and spectroscopy, DeVol et al. identified amorphous calcium carbonate from nacre growth fronts in sea snails. The amorphous precursors, which had previously been observed in calcitic biominerals such as sea urchin spicules, more closely resembled calcite than aragonite. Yet coral, which is also aragonitic, grows via an aragonitelike precursor. How nacre transforms calcite-like precursors into aragonite crystals remains unresolved.

J. Am. Chem. Soc. 10.1021/jacs.5b07931 (2015).

DNA Repair

A membrane scaffold for repairing DNA

Guy Riddihough

Many cellular processes inadvertently cause DNA damage, so cell survival critically depends on high-fidelity DNA repair. In Escherichia coli, the protein RecA plays a central role in repairing damaged DNA. RecA forms filaments on the ends of broken DNA, which allow the DNA repair machinery to search the genome for homologous sequences for accurate repair of the DNA break. Rajendram et al. now show that RecA interacts with specific lipids in the inner plasma membrane of E. coli. This membrane scaffolding acts to store RecA in the absence of DNA breaks. It also helps to nucleate and stabilize RecA filament bundles when breaks form, promoting DNA repair.

Mol. Cell. 10.1016/j.molcel.2015.09.009 (2015).

Structural Biology

Filling the structural landscape

Valda Vinson

Despite an ever-increasing number of high-resolution protein structures, as of 2013, about 40% of protein families had no representative structures, hindering understanding of their function. Ovchinnikov et al. take a step toward filling in this landscape by predicting structures for 58 of the 121 prokaryotic protein families with no known structures. They combined a recent version of Rosetta, which computes structures on the basis of an energy function, with amino acid residue contacts inferred from coevolution patterns in related protein sequences. The authors validated their methods by accurately predicting the structures of two proteins whose structures had previously been solved experimentally.

MOOCs: Retention versus achievement

Melissa McCartney

Massive open online courses (MOOC) open up higher education to citizens across the globe. As MOOCs continue to rapidly expand, the empirical research surrounding them strives to keep pace. Through examination of input characteristics, including learner demographics, prior experience, and self-reported commitment (data points that can be collected before the MOOC begins), Greene et al. provide insight into student retention and performance within the same MOOC. Coupled with survivor analysis, results showed that considerations such as intent to earn a certificate predicted retention, whereas the prior level of schooling predicted achievement. Depending on the goals of institutions interested in using MOOCs, data from this study can be used to determine whether any specific interventions should be implemented.

Am. Educ. Res. J.52, 925 (2015).

Materials Science

Grafting olefin polymers for stretchiness

Marc S. Lavine

Thermoplastic elastomers (TPEs) are stretchy rubberlike polymers that can be melt-processed, do not require cross-linking, and, unlike rubbers, can be recycled. Ohtaki et al. set out to create TPEs based solely on olefin polymers that would not require or be limited by the need for living polymerization processes. They grafted either isotactic or syndiotactic polypropylene segments to a backbone made from ethylene and α-olefins. The polypropylene is crystalline and imparts stiffness and a physical networks structure to the polymer, whereas the noncrystallizing backbone lets the polymer stretch. Samples showed up to 85% elastic recovery when stretched up to 1000%, rivaling the best linear block polyolefin TPEs.